The subject matter of the present disclosure broadly relates to the art of vehicle suspension systems and, more particularly, to a suspension system and method of operating the same for a vehicle having two or more rear axles. Such a system and method being capable of at least adjusting a height and/or orientation of the vehicle based at least in part on the relative position and/or orientation of the two or more rear axles with respect to one another and, optionally, with respect to the front axle of the vehicle.
The subject matter of the present disclosure finds particular application and use in conjunction with suspension systems of wheeled vehicles, and will be described herein with specific reference thereto. However, it is to be appreciated that the subject matter of the present disclosure is also amenable to use in other applications and environments, and that the specific uses shown and described herein are merely exemplary.
Specific reference is made herein to the term “axle,” which is used in conjunction with the present description and is to be broadly interpreted to generally denote any portion or portions of a vehicle that are operative to support an associated sprung mass between two or more ground-engaging components (e.g., wheels) of the vehicle. For example, an “axle” could be interpreted to be a rigid housing including one or more drive shafts and an optional differential or gear assembly. Such a construction is commonly used, for example, on a conventional cargo or utility truck. In this case, such an “axle” could be primarily responsible for transferring the load of the sprung mass from a set of springs to the ground-engaging components. In addition, such an axle could be adapted to transmit an engine torque to one or more of the ground-engaging components for propelling the vehicle.
An “axle” could also include the equivalent structures of the previous example but for an independent-type suspension system. As is commonly known in the art, the ground-engaging components of a vehicle having an independent suspension are capable of being vertically displaced independently from one another. An example of an independent suspension is that which is commonly used in the front and/or rear portions of a passenger-type vehicle. These independent suspension systems typically include upper and lower support arms and a wheel hub bearing assembly for transferring the vehicle mass to the associated wheels. Optionally, the wheel hub may include a universal or a constant velocity (CV) joint for receiving a drive shaft from a gearbox, transaxle, transfer case, or other powertrain component for propelling the vehicle. Even though the left front wheel, for example, may not be rigidly associated with the right front wheel of the passenger vehicle, an imaginary “axle” or “axis” can be defined between them. In such a case, the imaginary “axle” would extend from the point of rotation of the left wheel (i.e., proximal to a left wheel or hub bearing) to the point of rotation of the right wheel (i.e., proximal to a right wheel or hub bearing). During vehicle operation, the displacement of the imaginary “axle” would therefore be similar to that of the rigid-housing-type axle described previously. For these reasons, the use of the term “axle” is not intended to be limited to powertrain or driveline components or to limit the application of the instant invention to specific suspension system designs.
Additionally, specific reference is made herein to the terms “front axle” and “rear axle(s)” of a vehicle. For purposes of this disclosure, the front-most axle of a vehicle, which will commonly be a steering axle, is considered to be the “front axle.” Thus, any one or more axles that are rearward of the front-most axle are considered to be “rear axles”.
It is well known that land vehicles of most types and kinds are outfitted with a suspension system that supports a sprung mass of the vehicle (e.g., a body or chassis) on an unsprung mass of the vehicle (e.g., an axle or other wheel-engaging member). Known suspension systems typically include a plurality of spring elements (e.g., coil springs, leaf springs, torsion springs) that are responsive to forces and/or loads acting on the sprung and/or unsprung masses of the vehicle. Additionally, known suspension systems commonly include a plurality of damping members for dissipating energy inputs, such as the forces and/or loads acting on the sprung and/or unsprung masses of the vehicle.
In an effort to improve performance and/or ride quality of vehicles, suspension systems have been developed that utilize gas spring assemblies that are operative to adjust the height and/or orientation of the sprung mass with respect to the unsprung mass. As one example, such a known suspension system can include a set of front axle height sensors and a set of rear axle height sensors. The suspension system is adapted to monitor these height sensors while the vehicle is being operated. Generally, when a substantial difference is detected between the front and rear axles, the suspension system will selectively inflate or deflate one or more of the gas springs to adjust the sprung mass of the vehicle into the desired position and/or orientation. Doing so will often advantageously allow for a more even load distribution of the sprung mass over the unsprung mass.
However, such prior art suspension systems can also introduce certain problems and/or disadvantages that can be associated with or otherwise related to the actions of adjusting the position and/or orientation of the sprung mass relative to the unsprung mass of the vehicle. One such disadvantage is that prior art suspension systems are known to undertake height adjustment and/or leveling activities under conditions of operation in which it may be less desirable to do so, such as conditions in which the vehicle is undergoing a temporary or otherwise short term variation in height, for example.
To illustrate such a situation in greater detail, two different conditions of operation are shown in FIGS. 1 and 2. In FIG. 1, a vehicle VHC is shown in use on a relatively flat or smooth surface S (e.g., a conventional roadway) and operating in a first or smooth-surface operating state, in which a front axle FA, a first rear axle FRA and a second rear axle SRA are all generally disposed in approximate alignment within a first plane P1 that is approximately parallel to surface S. In this first operating state, a conventional suspension system would normally monitor one or more suitable height sensors (not shown) and selectively inflate or deflate one or more gas springs GSP of the suspension system to adjust the height and/or orientation of the sprung mass relative to the unsprung mass thereof.
In FIG. 2, however, a second or rough-terrain operating state is shown that illustrates first rear axle FRA of vehicle VHC as being disposed out of first plane P1 and within a second plane P2. Such a condition could be the result of a brief encounter with rough terrain or an otherwise imperfect or uneven surface D. In such a state, first rear axle FRA is no longer coincident or otherwise approximately aligned with front axle FA. As such, a conventional suspension system would be likely to undertake an action to adjust the position and/or orientation of the sprung mass. However, in many situations, such a condition will be a transient or otherwise temporary one. So, it may be undesirable to undertake a height adjustment or leveling action under such a condition.
Additionally, it will be recognized from FIGS. 1 and 2 that the position (and/or orientation) of the sprung mass (e.g., body BDY) of the vehicle relative to surface S will normally be approximately the same under both conditions, as indicated by dimensions DST, which dimensions are shown in FIGS. 1 and 2 as being approximately equal. Thus, under the condition illustrated in FIG. 2, it is possible that the sprung mass has not deviated from the desired position. As such, adjusting the gas springs to vary the height and/or orientation of the sprung mass under such conditions as are shown in FIG. 2 could undesirably result in an adjustment that moves the sprung mass away from the desired position and/or orientation, which deviation will be then be recognized by the suspension system once the transient height change has abated.
In an attempt to overcome the foregoing problems and/or disadvantages, some prior art designs have used momentary time delay processes and/or mechanical height averaging to minimize or reduce any over-responsiveness of the adjustment functions of the associated suspension system. However, these suspension systems have met with limited success, particularly in off-road applications in which long periods of time may be spent on substantially-rough terrain.
Accordingly, it is desirable to develop a vehicle suspension system and method of operating the same that overcomes the foregoing and other problems and disadvantages.